1. Field of the Invention
The present invention relates to a method for fabricating a circuit board. More particularly, the present invention relates to a method for fabricating a heat dissipation substrate.
2. Description of the Related Art
A chip generates heat in operation, and a chip with better performance generates more heat. However, excessive heat may cause overheating. If the heat cannot be dissipated quickly, the chip will not be able to work normally, or be damaged permanently. Furthermore, overheating may cause the packaging material and the circuit board to have different degrees of thermal expansion, such that the interface of different material will be broken, or the intensity of electrical connections of the elements and the circuit board will be impacted, allowing the product to crash.
To solve the abovementioned problem, a chip package carrier with a heat dissipation structure is developed to prevent overheating. In one of the prior art for heat dissipation, a heat dissipation lump (such as a copper block or a ceramics block) is first placed on a copper substrate, then, the insulation substrate (such as a polypropylene substrate), which includes a hole corresponding to the heat dissipation lump, is combined with the copper substrate which includes the heat dissipation lump, and, finally, another copper substrate is pasted on the other face of the insulation substrate. The heat dissipation lump is connected to the other copper substrate through the hole, and a follow-up process (such as the lithography and the etching) is executed. When the chip is placed on the copper substrate, the heat generated by the chip can be delivered to the other copper substrate for heat dissipation via the heat dissipation lump. However, in the abovementioned method, every step must be executed in alignment, and that may cause errors in alignment. The copper or ceramic block is formed by a mechanical treatment, but the mechanical treatment is difficult, and the yield rate is low. In addition, the thermal expansion coefficient of the ceramic block is quite different from those of the copper and the insulation. If the ceramic block, copper, and the insulation substrate undergo thermal expansion, the difference in degree of expansion will seriously distort the heat dissipation structure and make it stratified.
In another prior art for heat dissipation, a laser drilling process is used to form a plurality of laser holes on the substrate, and the holes are filled with thermally conductive material. When the chip is placed on the copper substrate, the heat generated by the chip can be delivered to the other face (such as the copper substrate) for heat dissipation via the thermally conductive material in the plurality of laser holes. However, the diameter of the laser hole is very small, and the heat dissipation performance is worse than the heat dissipation lump. Increasing the diameter of the laser holes to enhance the heat dissipation performance would greatly increase the cost in money and time.
Therefore, there is a need to provide a method for fabricating a heat dissipation substrate to solve the abovementioned problems.